Pulsed laser systems, such as excimer lasers, are well known. FIG. 1 is an end cross sectional view of a laser chamber, generally illustrated as 10, used in a conventional pulsed laser system. The laser chamber 10 comprises a pair of electrode members 12, which include a cathode 14 and an anode 16. The area between the cathode 14 and the anode 16 is referred to as an electrical discharge area 18. A support bar member 20 supports the anode 16. A heat exchanger 22, and a blower assembly 24 are also disposed within the laser chamber 10. As is well known by those skilled in the art, the pulsed laser system produces energy pulses from a gas mixture in the electrical discharge area 18. The mixture of gas, which typically includes krypton and fluorine, is maintained at a high pressure (e.g., 3 atm.). The electrode members 12 ionize the gas mixture to produce a high energy discharge.
The blower assembly 24 plays the important role of circulating the gases in the laser chamber 10 of the pulsed laser system. The circulation of the gases has many purposes, including maintaining the temperature of the gases at the most efficient level of reaction, maximizing the life cycle of the gases, and facilitating the overall operation of the pulsed laser system.
The blower assembly 24 comprises a plurality of blades or vanes 26 which are driven in a clockwise direction, as indicated by arrow 28, for circulating the gases about the laser chamber 10. The directional flow of the gases, as indicated by arrows 30, is through the electrical discharge area 18, with a clockwise circulation about the heat exchanger 22, and through the blower assembly 24. The gases pass between the blades 26 of the blower assembly 24, as illustrated by the arrow 30.
The support bar member 20, configured to support the anode 16, includes a cut-off point, as indicated by numeral 21. The cut-off point 21 is a general region on the support bar member 20, located adjacent to the blower assembly 24, which defines the inlet side and the outlet side of the blower assembly 24.
Each time one of the blades 26 passes the cut-off point 21, the support bar member 20 applies an aerodynamic load to the blower assembly 24. The aerodynamic load agitates the blower assembly 24, causing the blower assembly 24 to vibrate. As the rotational speed of the blades 26 increases, so does the aerodynamic load, and, thus, the vibration of the blower assembly 24. The effect of the rotational speed of the blades 26, i.e., the blower speed, on the vibration of the blower assembly 24 is illustrated in FIG. 2. Curve A illustrates the vibration response in the range of 2500 to 4000 vibrations per minute corresponding to blower speeds of 2500 RPM to 4000 RPM. Curve B illustrates the vibrational response associated with twice the rotational speed, and curve C illustrates the vibrational response associated with 23 times the rotational speed (i.e., 23 vanes or blades 26).
Furthermore, the vibration of the blower assembly 24 is highly detrimental to our application due to the nature of beam stability as it travels through. In the past any reduction of rotating mass vibration was necessarily associated with blower speed reduction. Blower speed reduction results in gas flow reduction. Gas flow reduction disabled the function of the laser. The vibration reduces the output efficiency of the blower assembly 24 by about 10%. The vibration also increases the noise produced by the blower assembly 24. Moreover, the vibration causes deterioration and failure of the mechanical components of the blower assembly 24, such as the blower assembly's 24 bearing members, driver shaft, and other moving components. As a result, it would be advantageous to reduce the vibration of the blower assembly 24.